Siblings of patients with rheumatoid arthritis have an increased mortality rate: a Swedish cohort study

OBJECTIVES: To estimate the mortality among siblings of patients with rheumatoid arthritis (RA) and put any excess mortality among these in relation to the mortality among patients with RA. METHODS: Using prospective nation-wide registers, we identified patients diagnosed with new-onset RA 2001–2017 (n=8137), patients with prevalent RA 2006–2017 (n=25 464), matched general population comparator subjects to all RA patients (n=22 457/68 674) and full-siblings of all groups (n=28 878/91 546). We followed all cohorts until death, 31 December 2018, migration and (for non-RA subjects) RA diagnosis. We compared patients with RA versus the general population, and siblings of RA versus siblings of the general population using Cox regression, including adjustment for socio-economy. RESULTS: The HR of death versus the general population was 1.11 (95% CI 1.01 to 1.22) for incident and 1.46 (95% CI 1.39 to 1.52) for prevalent patients with RA. The siblings of these patient groups were also at increased risk of death (HR=1.10, 95% CI 1.01 to 1.20 and 1.09, 95% CI 1.04 to 1.13, respectively), with little impact of adjustment for socio-economy. CONCLUSION: The mortality in RA is increased, but around one-fifth of this excess is present also among their siblings. Previous literature using general population rates for comparison has thus likely overestimated the direct impact on mortality attributable to RA. To bring down excess mortality in RA, optimal disease control is important but may not suffice.